I have been looking at company blogs to satisfy a mixture of professional and after-5 curiosities. The example I keep coming back to is 37signals.
The reasons they top my list are:
The product blog is a great read for hearing how to get the most out of their products. In their own words, Signal vs. Noise, a weblog by 37signals about design, business, experience, simplicity, the web, culture, and more.
For a tech R&D shop, this is about as good as I have seen. I'd also welcome comments on other good examples that people like!
An honourable mention goes to Art. Levedev Studio’s Life and Incredible Adventures of Optimus Keyboard blog where you can keep up with the hardware development in what may turn out to be the last word in keyboards!